There exist numerous applications for substantially optically transparent, electrically conducting films. Published U.S. Application No. 20040197546 ('546) to Rinzler et al., one of the present inventors, is entitled “Transparent electrodes from single wall carbon nanotubes”. '546 discloses a low temperature method of forming substantially optically transparent and electrically conductive single wall nanotube (SWNT) films.
'546 discloses uniformly suspending SWNTs in solution generally aided by a stabilizing agent (e.g. surfactant) followed by the deposition of the nanotubes onto the surface of a porous filtration membrane that possesses a high density of pores that are too small for the majority of the SWNTs to pass through. The nanotube film forms as an interconnected and uniform layer having the SWNTs generally lying on and being parallel to the membrane surface as the liquid is filtered away.
In one embodiment, the solution is vacuum filtered off, with the remaining SWNT film formed on the filter membrane surface. Any remaining surface stabilizing agent can be subsequently washed away and the film can then be allowed to dry. Significantly, the washing away of the stabilizing agents used to suspend the nanotubes permits the nanotubes to achieve intimate contact with each other (consolidated) throughout the body of the SWNT film. The nanotube film formed in this manner has one side intimately attached to the filtration membrane while the other side is uncoated. To make use of the film, it is generally necessary for the film be transferred to the desired substrate and to remove the membrane. This is accomplished by first adhering the free side of the nanotube film to the clean, desired substrate e.g. by pressure, followed by dissolution of the filtration membrane in a solvent in which the membrane is soluble.
The membrane material thus should be carefully selected. The membrane should tolerate the liquid in which the nanotubes are originally suspended, however the membrane should be soluble in a solvent to be removed that, ideally, does not chemically react with the substrate to which the SWNT film is to be attached. Dissolution of the membrane in this solvent leaves the nanotube film attached to the surface of the substrate. The '546 process can be extended to the deposition of materials other than nanotubes so long as 1) the material constituents can be uniformly suspended in a solution, 2) the liquid does not react with the selected filtration membrane material but passes through it, 3) the material constituents are retained on the membrane surface in the form of a film, and 4) the filtration membrane can be dissolved in solvent that does not dissolve the desired film, or the substrate, to which the film is to be transferred. For example, this method can thus also fabricate nanoparticle and nanowire thin films.